Without limiting the scope of the invention, its background is described in connection with an optical sensor that may be used to detect the presence of a given sample of interest such as a gas, liquid or solid.
Sensoring systems for refractive index measurements using critical angle are well known in the art, as are the principles of physics underlying the measurement of critical angle to determine refractive index of a medium. Critical angle is a function of refractive index. At angles of incidence larger than the critical angle, total internal reflection may be observed. Total internal reflection occurs when light rays are incident from a medium of a high index of refraction onto a medium of lower refractive index.
Devices in the prior art typically require a user to interpret the characteristic transition from transmission to total internal reflection; in most refractometers, a liquid is enclosed between two glass prisms and total internal reflection at the interface is observed visually.
Prior current liquid level sensors are sensitive only to the presence or absence of liquid in a given liquid chamber. They also require an optical medium of glass to be in the liquid chamber, which can effect changes in fluid flow patterns.
One embodiment of the present invention provides for detection of not only the presence of a liquid, but whether the liquid is sufficiently composed of a certain constituent. As such, the present invention is particularly useful in compressor operations, in which insufficient oil lubricant causes failure of the compressor. Among the many potential useful applications, the present invention may be used to prevent such failure by determining whether an oil reservoir containing an oil and refrigerant mixture has a sufficient percent composition of oil to keep it from malfunctioning. The present invention may also be employed in quality control applications to detect whether a solution falls below or exceeds a given threshold percentage of a component of interest.
Another limitation of the prior art sensors is that they are large and not fully integrated. The high number of independent components, interface structures, and additional circuitry increases total system cost and maintenance. The present invention solves many of these problems by integrating the electro-optic components within a single protective housing.
A sensing device that integrates the various electro-optical components on a single platform would be advantageous. The device should render data reflecting the critical angle at which total internal reflection is observed. The data should be available in either raw or processed format to permit further analysis by a personal computer or other similar processing system. A device that is small, lightweight and integrated would have widespread application and fill the void left by prior art sensors.